1. Field of the Invention
The present invention relates to a V belt type automatic transmission including a driving sheave mounted on a driving shaft, a driven sheave mounted on a driven shaft, a V belt extended between the driving sheave and the driven sheave, a thrust generating mechanism mounted on the driving shaft to produce a thrust for axially shifting an axially movable sheave part of the driving sheave to change the effective diameter of the driving sheave for automatic speed change.
2. Description of the Related Art
V belt type automatic transmissions are continuously-variable-speed transmissions used on four-wheel motor cars, such as all-terrain vehicles, motor scooters, and industrial vehicles including carriers. V belt type automatic transmissions are commonly called belt converters.
FIG. 7 shows a general power transmitting mechanism for vehicles, employing a V belt type automatic transmission. The V belt type automatic transmission includes a driving shaft 1 coupled with the crankshaft 7 of a prime mover (engine) 6, and a driven shaft 2 coupled with he input shaft of a gear transmission G. A driving sheave 3 and a driving sheave thrusting mechanism 19 are mounted on the driving shaft 1. A driven sheave 4 is mounted on the driven shaft 2. Driving sheave 3 has a fixed sheave part 10 mounted on the driving shaft 1 and is restrained from axial and rotational movement and a movable sheave part 11 mounted on the driving shaft for axial movement. The driving sheave thrusting mechanism 19 includes flyweights 16 supported for turning on the back surface of the movable sheave part 11, a pressure applying spring 20 biasing the movable sheave part 11 axially away from the fixed sheave part 10, and a spider 15 in engagement with a guiding projections 32 formed on the back surface of the movable sheave part 11 to transmit the torque of the driving shaft 1 to the movable sheave part 11 and to guide the movable sheave part 11 for axial movement.
The movable sheave part 11 is formed integrally with the guiding projections 32 and a cover 21. The cover 21 is stopped through a bearing 65 by a maximum driving sheave width adjusting mechanism 38 disposed on the right side, as viewed in FIG. 7, of the cover 21.
In this V belt type automatic transmission, the rotating speed of the driving sheave 3 varies delicately according to the variation of the torque of the prime mover 6 and, consequently, the guiding projections 32 of the movable sheave part 11 vibrate circumferentially relative to the spider 15 and strike against the spider 15 to generate hammering noise. Generally, such hammering noise can be reduced by accurately finishing the circumferentially opposite surfaces of the guiding projections 32 and the spider 15 so that gaps between the same circumferentially opposite surfaces are small. More positive measures use guide shoes 40 as shown in FIG. 8. FIG. 8 is a view taken along the direction of the arrow VIII in FIG. 7 and showing the engagement of the spider 15 and the guiding projections 32 of the movable sheave part 11 (FIG. 7). Guide shoes 40 each provided with a rubber layer 47 are interposed between the circumferentially opposite side surfaces 36 and 37 of the spider and the guide surfaces 32a and 32b of the guiding projections 32 on the opposite sides of the spider 15, respectively. The guide shoes 40 are able to slide axially along the guide surfaces 32a and 32b, and the rubber layers 47 eases impact resulting from the variation of the torque to reduce the hammering noise.
The reduction of the circumferential gaps between the spider and the guiding projections is limited because the guiding projections and the spider must slide axially relative to each other and it is difficult to reduce the hammering noise effectively by reducing backlashes to about zero.
Even if the shocks are eased by using the guide shoes 40 provided with the rubber layers 47, generation of hammering noise, though very light, is unavoidable because displacement of parts is unavoidable because the rubber layers 47 are inevitably subject to elastic deformation. Since the rubber layers 47 of the guide shoes 40 are permanently set in fatigue and the sliding surfaces of the guide shoes 40 are abraded during a long period of use and, consequently, hammering noise increases gradually with operating time.
The displacement of parts due to the elastic deformation of the rubber layers 47 promotes abrasion of the following parts in addition to the generation of hammering noise.
Parts that are abraded will be described with reference to FIG. 1 showing a V belt type automatic transmission according to the present invention. Parts that will be abraded are (1) a bushing 13 fitted in the bore of a movable sheave part 11, (2) a bushing 35 supporting a cover 21 formed integrally with the movable sheave part 11, (3) bushings 26 supporting flyweights 16, (4) bushings 29 supporting rollers 17 against which the flyweights 16 are pressed and (5) the contact surfaces of the flyweights 16 and the rollers 17. Related techniques are disclosed in JP-A No. Hei 9-317836.
It is an object of the present invention to eliminate the circumferential gaps to stop the hammering noise, maintaining the smooth axial movement of the movable sheave part relative to the spider by properly designing the shape of the guide shoes placed in the circumferential gaps between the movable sheave part of the driving sheave and the spider and to suppress the abrasion of the aforesaid parts.
To solve the problems, the present invention provides a V belt type automatic transmission comprising: a driving sheave mounted on a driving shaft and including a fixed sheave part mounted on the driving shaft and restrained from axial movement and turning relative to the driving shaft, and a movable sheave part mounted on the driving shaft for axial movement; a driven sheave mounted on a driven shaft; a V belt extended between the driving sheave and the driven sheave; and a thrust generating mechanism mounted on the driving shaft to produce a thrust for axially shifting the movable sheave part of the driving sheave, including flyweights supported for turning on the movable sheave part, and a spider having parts in contact with the flyweights, mounted on the driving shaft and restrained from axial movement and turning relative to the driving shaft; wherein guide shoes are disposed in circumferential gaps between the spider and the movable sheave part to guide the movable sheave part for axial movement relative to the spider, and the guide shoes have the shape of a wedge.
According to the present invention, the spider is provided with recesses for receiving the wedge-shaped guide shoes to hold the wedge-shaped guide shoes on the spider.
According to the present invention, the wedge-shaped guide shoes are biased radially outward with auxiliary biasing means, such as springs.